A. Field of the Invention
The present invention relates to an apparatus and method for imaging bodily tissue by using autofluorescence. More particularly, the present invention relates to an endoscopic apparatus and method for imaging and sampling bodily tissue using autofluorescence techniques.
B. Description of Related Art
Cervical cancer often begins as a precancerous lesion on the cervix (i.e., the outer end of the uterus) and is called cervical intraepithelial neoplasia (CIN). The lesion can deepen over a period of years and if left untreated can become an invasive cancer. A Pap smear test is currently a common method of providing a type of screening for cervical cancer. The test involves taking a sample of cells from the cervix, and sending the sample to a laboratory to be analyzed. Test results usually take two or three weeks to complete.
If the laboratory analysis determines that abnormal cells are detected from a first Pap test, a follow up test it typically performed. A second abnormal Pap smear will often prompt a colposcopic examination wherein the cervix is examined usually with a low-power stereo microscope. During colposcopy, suspect abnormal tissue is often biopsied and again sent to a laboratory for analysis. Because patients must often wait another two to three weeks for these results, a heightened period of anxiety and fear for the women and their families is created. Often, the first and second abnormal Pap smear result from false positive test results. Therefore, oftentimes, when a tissue sample has been biopsied, the sampled tissue was incorrectly determined to be cancerous and did not need to be removed. Spectroscopic autofluorescence, a minimally invasive procedure for analysis of cervical cytology, has been used to decrease a number of the problems normally associated with Pap smear tests.
Spectroscopic methods for differentiating cervical neoplasia from normal cervical tissue in vivo can be used to detect abnormal cells on the outside of the cervix. Typically, a fluorescence spectroscope has optical fibers at the end of a small probe which illuminate areas of the cervix. Suspect tissue is exposed to ultraviolet and visible laser or lamp light, causing substances naturally present in the tissue to fluoresce. The specific wavelength or signature of the light absorbed and emitted by cervical tissue is analyzed. The fluorescence spectra is then measured and compared at different intensities and wavelengths since abnormal or cancerous tissues consistently display different results from normal or non-cancerous tissue. Typically, a computer algorithm analyzes the fluorescence spectrum and assesses the degree of cell abnormality.
Generally, there are two types of fluorescence measurement techniques: the first being emission spectroscopy and the second being excitation spectroscopy. In emission spectroscopy, the exciting light is kept at a fixed wavelength and the emitted fluorescent intensity is measured as a function of the emitted wavelength. In excitation spectroscopy, the emission wavelength is kept fixed and the fluorescence intensity is measured as a function of the excitation wavelength.
Both emission and excitation spectra measurements have limitations. For example, both types of spectra measurements analyze only a single parameter to determine cell abnormality. The nature of the human tissue, however, is such that the application of any one single method produces a large amount of data, most of which is extraneous to the intended measurement. A primary reason for this situation is that tissues contain an extensive and diverse assortment of fluorescent species. Many of the species are present in high concentrations and have excitation bands distributed throughout the ultraviolet and the visible spectra regions.
Another limitation is that the emission band of one fluorophore may overlap the excitation band of another fluorophone, consequently leading to energy transfer between the emission and excitation bands. Consequently, emissions from one fluorophore could possibly excite another fluorophore. The net effect is that optically exciting a tissue sample at almost any wavelength in the ultraviolet or visible wavelength regions causes tissue autofluorescence over a broad spectral range. As these emissions are typically composed of contributions from multiple fluorophores, utilizing a single analytical parameter makes the autofluoresence spectrum complex and problematic to solve. Consequently, a robust discrimination between tissue states is often difficult to obtain.
Another limitation of typical fluorescence measurement techniques is that they cannot be readily combined with an apparatus or method for taking a biopsy. In other words, once an abnormal tissue area is detected, samples from this particular suspect area cannot be simply, quickly and accurately taken. With current devices utilizing fluorescent measurement techniques, after locating the abnormal area, the endoscope must be withdrawn from the patient. Once the endoscope is withdrawn, the Pap smear specimen can then be taken as a blind sample. Typically, there is no correlation between where on the cervix the sample is taken and where the suspect tissue was identified. Taking a blind sample, therefore, often results in samples being taken from normal areas or perhaps even areas which have not been previously investigated. Usually, the sample is also taken by relatively imprecise sampling devices such as brushes, scraper devices or the like.
Once the sample has been taken and withdrawn from the body, the specimen is typically smeared onto a microscope slide. This is often done by the physician performing the test. The slide is then submitted to a remote laboratory for cytopathological microscopic examination. Pertinent patient data must be sent along with the slide including the medical history, day in menstrual cycle, family history and other known risk factors. Gathering and collating these patient data, which are critical to the proper evaluation of a specimen, is a time-consuming, expensive, inefficient and labor-intensive process. The laboratory administrative personnel who gather such data are also responsible for manually recording the results of the Pap smear tests and ensuring that both the slide and paperwork provided to the cytotechnologist relate to the same patient. As the complexity of testing, analyzing, handling and transporting the Pap smear samples increases, the probability for a false positive, a false negative or sample contamination increases.
The typical Pap smear test has a number of other disadvantages. For example, in almost every instance where a slide specimen is produced, the slide is forwarded to a laboratory. No preliminary analysis to eliminate possible unnecessary laboratory testing is conducted. This increases the cost of performing a Pap smear since there is no preliminary determination as to the possibility of normality or absence of abnormality. Moreover, because the sampling is taken "blind", there is typically no assurance as to whether the suspect abnormal cells have in fact been sampled. Oftentimes, only after having forwarded the sample to the testing facility and waiting two to three weeks is it eventually determined that another sample must be taken. Incidents of poor sample or slide preparation are also common because of the large amount of human interface with each specimen slide. Moreover, because slides are often sent to a location remote, there is an increased risk that the sample may become lost, broken or contaminated. The complexity of maintaining a secure and sterile transporting medium further increases the cost of sample transport. In addition, there is a psychological disadvantage in having to wait up to two weeks or longer for the test results to either confirm or rebut a primary abnormal reading.